Studies on the ability of multicellular organisms to tolerate specific environmental extremes are relatively rare compared to those of unicellular microorganisms in extreme environments. Tardigrades are extremotolerant animals that can enter an ametabolic dry state called anhydrobiosis and have high tolerance to a variety of extreme environmental conditions, particularly while in anhydrobiosis. Although tardigrades have been expected to be a potential model animal for astrobiological studies due to their excellent anhydrobiotic and extremotolerant abilities, few studies of tolerance with cultured tardigrades have been reported, possibly due to the absence of a model species that can be easily maintained under rearing conditions. We report the successful rearing of the herbivorous tardigrade, Ramazzottius varieornatus, by supplying the green alga Chlorella vulgaris as food. The life span was 35 +/- 16.4 d, deposited eggs required 5.7 +/- 1.1 d to hatch, and animals began to deposit eggs 9 d after hatching. The reared individuals of this species had an anhydrobiotic capacity throughout their life cycle in egg, juvenile, and adult stages. Furthermore, the reared adults in an anhydrobiotic state were tolerant of temperatures of 90 degrees C and -196 degrees C, and exposure to 99.8% acetonitrile or irradiation with 4000 Gy (4)He ions. Based on their life history traits and tolerance to extreme stresses, R. varieornatus may be a suitable model for astrobiological studies of multicellular organisms.

M. tardigradum survives high doses of ionizing radiation in both hydrated and anhydrobiotic states, but irradiation with >1000 Gy makes them sterile.

Shiga toxin (Stx) is an enterotoxin produced by Shigella dysenteriae serotype 1 and enterohemorrhagic Escherichia coli, which binds specifically to globotriaosylceramide, Gb3, on the cell surface and causes cell death. We previously demonstrated that Stx induced apoptosis in human renal tubular cell line ACHN cells (Taguchi, T., Uchida, H., Kiyokawa, N., Mori, T., Sato, N., Horie, H., Takeda, T and Fujimoto, J. (1998) Kidney Int. 53, 1681-1688). To study the early signal transduction after Stx addition, Gb3-enriched microdomains were prepared from ACHN cells by sucrose density gradient centrifugation of Triton X-100 lysate as buoyant, detergent-insoluble microdomains (DIM). Gb3 was only recovered in DIM and was associated with Src family kinase Yes. Phosphorylation of tyrosine residues of proteins in the DIM fraction increased by 10 min and returned to the resting level by 30 min after the addition of Stx. Since the kinase activity of Yes changed with the same kinetics, Yes was thought to be responsible for the hyperphosphorylation observed in DIM proteins. Unexpectedly, however, all of the Yes kinase activity was obtained in the high density, detergent-soluble fraction. Yes was assumed to be activated and show increased Triton X-100 solubility in the early phase of retrograde endocytosis of Stx-Gb3 complex. Since Yes activation by the Stx addition was suppressed by filipin pretreatment, Gb3-enriched microdomains containing cholesterol were deeply involved in Stx signal transduction. Shiga toxin (Stx)1 of Shigella dysenteriae serotype 1 and enterohemorrhagic Escherichia coli is one of the major cause of hemolytic uremic syndrome (HUS). Stx consists of an A subunit of 32 kDa associated with five B subunits of 7.5 kDa each. The A subunits act to remove the adenine base at position 4324 of 28 S rRNA and are responsible for inactivation of protein synthesis and toxicity (2). The A subunits lacking B subunits, however, do not show any toxicity because of their inability to bind to the cell surface receptor. The B subunits bind specifically to cell surface glycosphingolipid (GSL) receptors-Gb3, 2 also known as CD77 or blood group P k (3). Once Stx is internalized, protein synthesis is suppressed, leading to cell death.Cell death is widely known to take place through two distinctive processes, necrosis or apoptosis. In contradiction to Williams's report (4), a number of recent studies have clearly demonstrated that Stx induces apoptosis in several different cell types, including Burkitt's lymphoma cells (5), Vero cells (6), human renal tubular derived ACHN cells (1), and normal human renal tubular epithelial cells (7,8). Especially, the later two studies indicate the importance of apoptotic cell death as one mechanism of damage to renal epithelium in the pathogenesis of HUS. Although the B subunit has no inhibitory effect on protein synthesis, a series of studies indicates that it alone participate to transduce cell signaling and can induce apoptosis in some instances such as Burkitt's lymphoma (5, 9). These reports en...

The contribution of histone H1 to mitotic chromosome condensation was examined with the use of a cell-free extract from Xenopus eggs, which transforms condensed sperm nuclei into metaphase chromosomes. When H1 was removed from the extract, the resultant metaphase chromosomes were indistinguishable from those formed in complete extract. Nucleosomal spacing was the same for both. Thus, H1 is not required for the structural reorganization that leads to condensed metaphase chromosomes in this egg extract.